The Koch Brothers—more specifically the company Koch Carbon, owned by Charles and David Koch—ship and sell the stuff as a low-grade alternative to coal.

And Ambassador Bridge owner Matty Moroun also owns the land that Detroit’s biggest coke piles are now sitting on (though it’s handled by a different company, Detroit Bulk Storage).

Activists are worried about pet coke’s health and environmental impacts, especially since it’s still being stored in uncontained piles on the riverfront. But they’re also concerned about the larger impacts of tar sands oil flowing into the US from Canada.

Activists issued a list of demands. Some were grand in scale—halting the flow of tar sands altogether, and transitioning away from fossil fuels.

Others were more locally-focused, like demands that residents living near the coke piles be given access to baseline health tests, and that Marathon and other industries pay into a community health fund.

Many simply feel like Detroit's riverfront is being treated as a dumping ground.

A spokesman for the pet coke’s handlers at the site, Detroit Bulk Storage, says they’re working to address environmental and health concerns about the pet coke. They’ve begun spraying the piles with a sealing epoxy to make sure dust doesn’t escape, and have taken steps to seal the ground around the piles so there’s no contaminated runoff.

Anti-tar sands activists, whose campaign against the Detroit pet coke piles has drawn national and international attention, appeared to score a minor victory last week.